A mouse genomic clone (designated 1A-1) with strong sequence complementarity to the adult glycerol-3-phosphate dehydrogenase gene (Gdc-1, chromosome 15) was isolated from a BALB/c embryo DNA library. Clone 1A-l was recognized by a unique-sequence 882 bp Gdc-I subclone (pO.8H) derived from the second exon and flanking introns. Clone 1A-1 cross-hybridized with three exon-specific probes from Gdc-l, yet possesses a restriction map which is completely different. Southern blot analysis of Bam H1 digested BALB/cJ DNA probed with pO.8H identified both a 5.1 Kb band predicted by the Gdc-1 restriction map, and a 3.2 Kb band predicted by the restriction map of clone 1A-1. These observations support the hypothesis that clone 1A-1 represents the embryonic glycerol-3-phosphate dehydrogenase gene (Gdc-2, chromosome 9). The proposed research will focus on further characterization of this clone by DNA sequence analysis and chromosomal mapping to verify its tentative identification as the embryonic GPDH gene. Additional genomic clones containing the remaining 3' end of this gene will also be isolated and sequenced, leading to a complete determination of the structural organization of this gene. Positive identification of this gene as Gdc-2 will result in a complete knowledge of the structural organization of both the adult and embryonic glycerol-3-phosphate dehydrogenase genes of the mouse. This information represents an essential first step in determining the molecular mechanisms controlling the tissue-specific and developmental stage-specific expression of these genes. In addition, as a result of the large degree of linkage conservation and DNA sequence conservation between mice and humans, the positive identification of a mouse embryonic glycerol-3-phosphate dehydrogenase gene would facilitate the mapping and sequencing of corresponding regions of the human genome.